High-pressure steam drive oil production process



Nov. 21, 1967 R. v. SMITH 3, 5

HIGH-PRESSURE STEAM DRIVE OIL PRODUCTION PROCESS Filed Sept. 11, 19645.5- ;.4- U .3- C! a FIG. 2

O l n 1 1 I 1 o24ee|o |4|e|a2o PATTERN AREA (ACRES) Z .5 t,.4- F/GJINVENTOR. l R.V. SMITH I l l O l l BY o 2 4 s 8 IO l2 l4 l6 I8 20 WPATTERN AREA (ACRES) A T TORNEVS United States Patent Oflice 3,353,598Patented Nov. 21, 1967 3,353,598 HIGH-PRESSURE STEAM DRIVE OILPRODUCTION PROCESS Robert V. Smith, Bartlesville, Okla, assignor toPhillips Petroleum Company, a corporation of Delaware Filed Sept. 11,1964, Ser. No. 395,866 7 Claims. (Cl. 16611) This invention relates to aprocess for producing oil from a partially depleted reservoir by theinjection of high pressure steam into the reservoir.

One of the unsolved problems in the production of oil from oilreservoirs is the recovery of substantially all of the oil from anygiven reservoir. To illustrate, the Burbank Field in Oklahoma has beencontinuously produced for approximately 40 years and some sections ofthe field contain substantially as much as has been produced therefrom.To be specific, a substantial section of the Burbank Field which has aporosity of 21 percent has an oil saturation at the present time of 46percent. Primary production in this field terminated several years agoand gas drive followed by water drive have been applied as secondaryrecovery methods. While substantial quantities of oil have been producedfrom the Burbank Field by these secondary recovery methods, it stillremains that the oil saturation throughout the field is appreciable,amounting to 46 percent saturation in a substantial section thereof,which challenges oil production workers in the art and renders solutionof the production problem significantly remunerative.

This invention is concerned With a unique method of recovering oil froma partially depleted reservoir or oilbearing stratum which has defiedordinary secondary oil production methods such as water flooding and gasdrive.

Accordingly, it is an object of the invention to provide a unique methodof secondary oil production utilizing high pressure steam injection.Another object is to provide a process for secondary oil recovery whichcombines certain aspects of water flooding and steam injection. Afurther object is to provide a process for secondary oil recoveryutilizing steam injection which makes eflicient -use of the size of theproduction pattern. Other objects .of the invention will become apparentto one skilled in the art upon consideration of the accompanyingdisclosure.

Abroad aspect of the invention comprises subjecting a partially depletedreservoir or oil-bearing stratum to water flooding to further partiallydeplete same, injecting high pressure steam into the water flooded areadefined by a specific well pattern until asubstantial portion but notall of the available pore space in the well pattern has been filled withsteam, and thereafter driving the heat front and steam thru the wellpattern to the production wells therein so as to produce the steamed-outoil from the pattern. A significant aspect of the invention comprisesbuilding up a substantial reservoir pressure during the water floodingphase of the process and maintaining this water pressure in the area ofthe stratum surrounding the pattern thru which steam is driven so thatthe oil steamed out by the steam flood is squeezed into the productionwells bythe combination of steam pressure and resisting water pressuresurrounding the steam flood pattern. This solves the problem frequentlyencountered wherein'the secondary recovery drive forces oil out of thewell pattern and leaves pockets of oil unrecovered in the reservoir.

The injection of water after the steam injection to drive the steam andthe heat in the stratum thru the well patern has a significantlybeneficial effect in that no steam is bypassed and the condensation ofpockets of steam behind the driving front is avoided. This type ofcondensation greatly reduces the pressure in the condensation area andsucks in oil from surrounding areas which creates oil pocketsunrecovered by the drive of the steam front. The injection of water atnormal reservoir temperature assures proper driving of the steam andheat front thru the production pattern and effects substantially all ofthe steam condensation at the interface of the water and steam, therebyavoiding later condensation of steam behind the driving front orwater-steam interface.

The invention is more fully described by reference to the accompanyingschematic drawing of which FIGURE 1 is a plan view of a partiallydepleted reservoir illustrating one well pattern particularly adapted tosecondary recovery by steam injection following water flooding; FIGURE 2is a plot of a curve showing the relationship between the pattern areain acres and the fraction of steam-out time during which steam must beinjected; and FIGURE 3 is a plot of a curve showing the relationshipbetween the pattern area in acres and the fraction of the pattern volumewhich must be filled with steam.

In FIGURE 1, an oil field outline is identified by the numeral 10. Asubstantial section of the field indicated by numeral 12 is of higheroil concentration than the surrounding field. Water flooding has beenapplied to substantially the entire field 10 thru conventional wellpatterns not shown. Wells 14, 16, and 18 are Wells in the primaryproduction pattern and also in the Water flooding pattern. Injectionwell 20 was drilled specifically for the steam injection phase of therecovery process.

During the water flooding phase of the secondary recovery program, waterpressure within the field was built up to approximately 1000 p.s.i. andthis pressure was substantially maintained for the steam injection andsteam drive phases of the recovery process. The injection of steam thruinjection well 20 in a specific embodiment of the invention is at apressure of about 1700 p.s.i. (temperature 613 F.) at a rate of about23,000 lbs. of steam per hour. The Burbank sand, which field 10represents. is 'a consolidated sand containing natural horizontalfractures. In strata which unduly limit steam injection rates,horizontal fracturing should be applied before steam injection isattempted. The well pattern formed by wells 14, 16, 18, and 20 has anarea of about 4.37 acres and the triangular pattern is about 680 feet oneach side. Well 20 is at substantially the geometric center of thepattern. About .43 or 43 percent of the pattern volume is flooded withsteam before initiating the water drive. This value is read directlyfrom FIGURE 3 which shows the relationship between the pattern area inacres and the fraction of the pattern volume which must be filled withsteam if the steam and water are to arrive at the production wellssubstantially simultaneously. This represents the most eflicient use ofsteam and water in the steam-andwater drive phases of the process. Ifless steam is utilized, all of the steam is condensed before the waterand steam arrive at the production wells and, if more steam is injected,the steam phase reaches the production wells substantially ahead of thewater front. The volume of steam injected is in the range of about 0.2to 0.65 pore volume of the well pattern.

A fraction of the steaming-out period, i.e., the time elapsed frominitial steam injection until steam arrives at the production wells, inthe pattern of FIGURE 1 under the conditions set forth, is 0.37 or 37percent of the total steam-out time. This is read from FIGURE 2 for awell pattern of 4.37 acres under the conditions set forth. The curves ofFIGURES 2 and 3 were plotted using the method disclosed by I. W. Marxand R. H. Langenheim in Petroleum Transactions, AIME, volume 216, 1959,pp. 312-315.

The water is injected following the steam injection period at reservoirtemperature and at a rate of about 5,000 bbL/day. Under these conditionsthe steam-out time is about 1.15 years. The oil saturation in the steamproduction pattern is about 46 percent with 21 percent porosity and theoil saturation after the steaming-out period is in the range of 8-12percent.

While specific values have been given to illustrate the technique of theinvention in a specific reservoir situation, these values may be variedsubstantially within the scope of the invention. The steam injectionrate may be varied in the range of 12,000 to 50,000 lbs/hr. of steamdepending upon the porosity of the stratum, the characteristics of theoil in place, and the character of the stratum immediately surroundingthe injection well. For high injection rates, fracturing should beresorted to. The steam injection pressure may be varied in the range of750 to 3000 psi, the temperature depending upon the injection pressure.The size of the well pattern for most efiicient utilization of steam isin the range of 112 acres. Larger well patterns than 12 acres may beutilized but the efficiency and heat losses indicate the use of moredesirable smaller acreages. Utilizing production patterns in the rangeof 1-12 acres required steam injection periods in the range of 2065percent of the total steam-out period. Larger acreages require higherpercentages of steam injection periods. The water injection rate may bevaried in the range of 2500 to 15,000 bbl./day and will depend upon thepattern area being produced as well as the conditions of the stratum inwhich the process is being effected. Water-injection pressure in therange of about 500 to 2000 p.s.ig is used.

While a 4-sp0t well pattern is illustrated herein, other well patternsare utilizable including a 5-, 6-, 7-, 8-, or 9-sp0t pattern. It is alsofeasible to utilize a line of steam injection wells flanked on eitherside by parallel lines of production wells as is conventional in linedrive production.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A process for producing oil from an oil-bearing stratum which hasbeen produced by natural fluid drive comprising the steps of:

(a) water flooding a well pattern penetrating said stratum by injectingwater under pressure into at least one injection well in said pattern tobuild up substantial pressure within the well pattern and in thesurrounding stratum and producing fluids including oil thru at least oneproduction well therein;

(b) following step (a), without substantial reduction of pressure, steamflooding said pattern by injecting steam at a pressure substantiallyabove stratum pressure at the end of step (a) thru at least oneinjection Well in said pattern and producing fluids including oil fromat least one production well in said pattern, the volume of the injectedsteam being in the range of about 0.2 to 0.65 of the pore volume of saidpattern;

(c) following step (b), terminating steam injection and driving injectedsteam thru said pattern with cool fluid to drive a resulting hot zonetoward the production well(s) of step (b); and

(d) recovering fluids including oil from the production well(s) of step(b) produced by step (c).

2. The process of claim 1 including the step of driving fluids includingoil from said pattern by a gas drive intermediate natural fluid driveand step (a).

3. The process of claim 1 wherein step (c) is efiected by a water drivefree of gas at an injection rate in the range of about 2500 to 15,000bbl./day.

4. The process of claim 1 wherein said injection well in step (b) is acentral well and the production wells are ring wells and including thesteps of:

(e) selecting said well pattern surrounded by oil-bearing stratum;

(f) building up stratum pressure during step (a) to the range of 500 to2000 p.s.i. by water injection;

(g) maintaining stratum pressure in the range of step (f) during steaminjection of step (b) and during the drive of step (c) so as to squeezestratum fluids toward last said production wells.

5. A process for producing oil from an oil-bearing stratum followingprimary production thereof comprising the steps of:

(a) waterflooding a substantial section of said stratum by injectingwater under a pressure in the range of about 500 to 2000 psi. thru atleast one injection well and producing oil thru at least one productionwell and building up a pressure in said range throughout a substantialpressure area;

(b) selecting a well pattern including a central injection well and atleast 3 surrounding production wells within the pressure area of (a);

(c) without substantially reducing pressure established in step (a),injecting steam thru the injection well of step (b) while substantiallymaintaining the stratum pressure of step (a) until a volume of steamequal to a substantial portion but less than all of the pore volume ofthe well pattern of (b) has been injected, said steam being injected ata pressure in substantial excess of the pressure established in step (d)driving the injected steam of step (c) and a resulting hot zone towardthe production wells of step (b) with a cool driving fluid so as toproduce oil therein while maintaining substantially the stratum pressureof step (a); and

(e) recovering oil from the production wells of step (b) produced by theprocess.

6. The process of claim 5 wherein the well pattern of step (b) covers anarea in the range of about 1 to 12 acres, the steam injection pressureis in the range of about 750 to 3000 p.s.i.; and the pore volume in thewell pattern filled with steam is in the range of about 0.2 to 0.65 ofthe pore volume in said well pattern.

7. The process of claim 6 wherein said well pattern is in an island ofsaid stratum of higher permeability and higher oil saturation than thesurrounding stratum.

References Cited UNITED STATES PATENTS 2,813,583 11/1957 Marx et al.16611 2,876,838 3/1959 Williams 166-11 3,027,942 4/1962 William et al.16611 3,036,632 5/1962 Koch et al. 16611 3,042,114 7/1962 Willman 16611FOREIGN PATENTS 511,768 8/1939 Great Britain.

CHARLES E. OCONNELL, Primary Examiner.

STEPHEN J. NOVQSAD, Examiner,

1. A PROCES FOR PRODUCING OIL FROM AN OIL-BEARING STRATUM WHICH HAS BEENPRODUCED BY NATURAL FLUID DRIVE COMPRISING THE STEPS OF: (A) WATERFLOODING A WELL PATTERN PENETRATING SAID STRATUM BY INJECTING WATERUNDER PRESSURE INTO AT LEAST ONE INJECTION WELL IN SAID PATTERN TO BUILDUP SUBSTANTIAL PRESSURE WITHIN THE WELL PATTERN AND IN THE SURROUNDINGSTRATUM AND PRODUCING FLUIDS INCLUDING OIL THRU AT LEAST ONE PRODUCTIONWELL THEREIN; (B) FOLLOWING STEP (A), WITHOUT SUBSTANTIAL REDUCTION OFPRESSURE, STEM FLOODING SAID PATTERN BY INJECTING STEAM AT A PRESSURESUBSTANTIALLY ABOVE STRATUM PRESSURE AT THE END OF STEP (A) THRU ATLEAST ONE INJECTION WELL IN SAID PATTERN AND PRODUCING FLUIDS INCLUDINGOIL FROM AT LEAST ONE PRODUCTION WELL IN SAID PATTERN, THE VOLUME OF THEINJECTED STEAM BEING IN THE RANGE OF ABOUT 0.2 TO 0.65 OF THE POREVOLUME OF SAID PATTERN; (C) FOLLOWING STEP (B), TERMINATING STEAMINJECTION AND DRIVING INJECTED STEAN THRU SAID PATTERN WITH COOL FLUIDTO DRIVE A RESULTING HOT ZONE TOWARD THE PRODUCTION WELL(S) OF STEP (B);AND (D) RECOVERING FLUIDS INCLUDING OIL FROM THE PRODUCTION WELL(S) OFSTEP (B) PRODUCED BY STEP (C).